1. Field of the Invention
The present invention relates to a thin-walled, tubular hollow profile, particularly a spacer tube for the production of spacer frames of insulated glazing, as well as to a method and a device for its production.
2. The Prior Art
Conventional insulated glazing has at least two panes of glass disposed parallel to and spaced apart from one another, between which a pane interstice having a defined width is provided. In order to permanently guarantee this predefined pane interstice, a circumferential space holder frame is provided between the two glass panes, which frame connects the two glass panes with one another in the region of their outer pane edges. In this connection, the spacer frame consists of a thin-walled spacer tube having an essentially flat rectangular cross-section, which was bent accordingly to form the spacer frame. Alternatively, the spacer frame consists of multiple individual spacer tubes, which are set onto one another via corner connectors.
Such spacer tubes are hollow profiles made of aluminum, for example, which are produced for example, by means of bending by rollers and subsequent welding of the abutting longitudinal edges of the aluminum strip. These spacer tubes have a wall thickness of 0.3 mm to 0.6 mm. Because of the good heat conductivity of aluminum, however, these spacer tubes made of aluminum have the disadvantage that the region of the outer pane edges, i.e. the pane border region, cools greatly at low outside temperatures. As a result, valuable heat energy is lost. If the temperature furthermore drops to below the dew point in this region, condensate forms, and this condensate can damage the frame construction, particularly in the case of wooden windows.
In order to reduce these effects, more and more spacer tubes made of materials that have clearly lesser heat conductivity have been in use since approximately the mid-1990s, and particularly within the course of the energy savings regulations (EnEV) that went into effect in 2002. In this connection, the term “warm edge” was coined. This term is used for the region of an insulated glazing in which the outer pane edges are connected with one another by means of the spacer tubes, whereby the spacer tubes consist of a material having low heat conductivity.
For example, such spacer tubes consist of stainless steel and have a wall thickness of 0.15 mm to 0.2 mm. These stainless steel spacer tubes are also produced from a stainless steel strip, by means of bending by rollers and subsequent welding of the abutting longitudinal edges of the strip. The spacer tubes made of stainless steel are characterized in that they can be easily processed further, particularly by machine. The spacer tubes can be cut to the correct length and bent to form the spacer frames, in simple manner. The material costs of stainless steel in particular, however, have increased tremendously in recent years.
Furthermore, spacer tubes made of plastic exist, which are produced by means of extrusion. Spacer tubes made of polymer materials having low heat conductivity values have a lower heat passage coefficient in comparison with spacer tubes made of stainless steel. Although such spacer tubes can be produced more cost-advantageously, further processing, particularly bending to form the spacer frames, is difficult. Furthermore, plastic is not ultra-violet (UV) ray resistant, tends to age, and is not completely diffusion-tight. For this reason, it is known to cover the backs of the spacer tubes with a metallic foil. The foil acts as a diffusion barrier. The other stated disadvantages of the spacer tubes made of plastic, however, are not eliminated with this cover.